The present invention relates to an image displaying apparatus of a processed image from temporally sequential images. More particularly, the present invention relates to a technique by which a change in a radiographic object caused with the lapse of time is clearly shown in accordance with a processed image from temporally sequential images obtained when a plurality of temporally sequential images are subjected to image processing.
Radiographic images such as X ray images are frequently used for the diagnosis of a disease. In order to obtain X ray images, film-screen systems are conventionally used. In a film-screen system, X rays that have been transmitted through a radiographic object are irradiated on a phosphor layer (phosphor screen) so that visible luminescence is generated from the phosphor layer. The thus generated visible luminescene is irradiated on a silver halide film.
Using radiographs obtained in the above manner, medical diagnosis is conducted by a doctor as follows. For example, a plurality of radiographs are taken of the same patient at different points of time. After a plurality of radiographs have been obtained, for example, after chest radiographs of a patient to be examined have been taken in a routine medical checkup, the radiographs are observed by a doctor using a viewing box. In the process of observation, the doctor checks the temporally sequential images, and in accordance with his experience, he recognizes a change caused with the lapse of time, which is called an interval change. The result of observation is used for the medial diagnosis.
The above method in which temporally sequential images are compared with each other is called comparison reading. The method is important to find a change newly caused by a disease and also to recognize a progress or improvement of a disease.
However, even when the temporally sequential images are compared with each other in the above manner, an important interval change caused by a disease may be overlooked in some cases.
For example, bones, blood vessels, bronchus and other anatomic structures are sometimes combined with each other in a complicated manner on a radiographic image of the chest. Therefore, it is sometimes difficult to find a change on the image caused by a disease, because the change is camouflaged by the normal anatomic structures of bones, blood vessels, bronchus and other anatomy. Further, the density and contrast of two radiographs are usually different from each other due to the difference of an amount of exposure of X rays irradiated in the process of radiographing. Because of the fluctuation of density and contrast on the temporally sequential images on two radiographs, it is difficult to compare the two temporally sequential images with accuracy.
In comparison readings, it is necessary to select the films stored in a storage and bring them back to the reading room. Further, it is necessary to set the films on the viewing box prior to observation. This is inefficient in terms of time and labor.
According to the conventional method, moreover, even if a portion in which an interval change caused by a disease is found, it is necessary for the doctor to use his experience and knowledge for recognizing and judging the accurate position, range and degree of the change on the image caused by a disease. Therefore, the conventional technique makes it difficult to enhance the efficiency of medical diagnosis.